In recent years, OCT has attracted attention which forms an image that represents surface and/or internal morphologies of an object using light beams from a laser light source etc. Unlike X-ray CT, OCT is noninvasive to human bodies and is therefore expected to be utilized in medical and biological fields in particular. For example, in ophthalmology, apparatuses for forming images of a fundus, a cornea, etc. are in practical stages.
An apparatus disclosed in Patent Document 1 uses so-called “Fourier Domain OCT” technique. More specifically, this apparatus irradiates an object with low-coherence light beam, superposes its reflected light and reference light to generate interference light, and acquires spectral intensity distribution of the interference light, and executes Fourier transform to form an image that represents morphology of the object in a depth direction (z-direction). Further, this apparatus is provided with a galvano mirror for scanning light beams (signal light) along one direction (x-direction) perpendicular to the z-direction, and with this, forms an image of a desired measurement targeted region of the object. An image formed by this apparatus is a two-dimensional cross-sectional image along the depth direction (z-direction) and scanning direction (x-direction) of the light beam. Such a technique is specifically called Spectral Domain.
Patent Document 2 discloses a technique that scans signal light in horizontal and vertical directions (x-direction and y-direction) to form a plurality of two-dimensional cross-sectional images along the horizontal direction, and acquires three-dimensional cross-sectional information of a measured area based on these cross-sectional images to perform imaging. Such three-dimensional imaging techniques include, for example: a method of arranging and displaying a plurality of cross-sectional images (referred to as stack data etc.); a method of generating volume data (voxel data) based on stack data, performing rendering on the volume data to form a three-dimensional image; and the like.
Patent Documents 3 and 4 disclose other types of OCT. An apparatus disclosed in Patent Document 3 scans wavelengths of light irradiated to an object (wavelength sweeping), detects interference light obtained by superposing reflected lights of the respective wavelengths on reference light to acquire spectral intensity distribution, and executes Fourier transform on it to image morphology of an object. Such an apparatus is called Swept Source type etc. Swept Source is a kind of Fourier Domain.
An apparatus disclosed in Patent Document 4 irradiates an object with light with predetermined beam diameter, and analyzes components of interference light obtained by superposing reflected light thereof and reference light to form an image of the object in a cross section orthogonal to traveling direction of the light. Such an apparatus is called Full-Field type, En-face type, or the like.
Patent Document 5 discloses an example of OCT application to ophthalmology. Before OCT was utilized, a retinal camera, a slit lamp microscope, a scanning laser ophthalmoscope (SLO) etc. were used for observing eyes (see Patent Documents 6 to 8 for example). A retinal camera photographs a fundus by irradiating an eye with illumination light and receiving reflected light thereof from the fundus. A slit lamp microscope obtains a cross-sectional image of a cornea by cutting off a light section of the cornea using slit light. An SLO images morphology of a retinal surface by scanning the fundus with laser light and detecting reflected light thereof using high-sensitive elements such as a photomultiplier.
OCT apparatuses have advantages over retinal cameras etc. in that a high-definition image may be obtained, a cross-sectional image and a three-dimensional image may be obtained, and the like.
In this way, OCT apparatuses can be used for observing various sites of an eye and is capable of obtaining a high-definition image; therefore, they have been utilized for diagnoses of various ophthalmologic disorders.